When line of sight detection or facial expression detection is performed from a face image under circumstances where it is difficult to secure sufficient illuminance like at night or in tunnels, a floodlight may be used to secure illuminance. In the case of using a floodlight, a cornea-reflected image generated as floodlight is projected on a cornea of an eyeball is observed on the eyeball. When an image of the cornea-reflected image (which may be hereinafter referred to as “cornea-reflected image”) overlaps a pupil image, the pupil image may be hidden by the cornea-reflected image. Under this circumstance, it is difficult to detect the pupil image by a conventional pupil detecting technique, which is premised on the assumption that the pupil image is completely seen.
As a first method of coping with this problem, there is a method disclosed in Patent Literature 1. In the first method, a distribution of luminance in an eye area is calculated, and a negative edge and a positive edge corresponding thereto are searched based on a calculation result. In the above-described way, even though the cornea-reflected image appears in the pupil image, pupil detection can be performed.
Further, as a second method, there is a method disclosed in Patent Literature 2. In the second method, a super luminescent diode (SLD) is used as a floodlight. Thus, an area of a reflected image of a floodlight projected on glasses or the cornea can be reduced, and therefore pupil detection can be stably performed.
Furthermore, as a third method, there is a method disclosed in Non-Patent Literature 1. In the third method, a plurality of parallelograms are formed from edges of a pupil area, and voting is performed on the centers of the parallelograms. Then, the most voted coordinates are detected as the pupil center. Then, a pupil contour is detected from edges which are at equal distances from the detected pupil center.